The liquid crystal display (LCD) devices characterized by compact size and lighter weight are widely applied to various electronic devices, such as personal computers, laptop computers, mobile phones, and personal digital assistants. Take a transmission type LCD for example, the LCD device itself does not emit light, and therefore a separate light source is required to emit light. The light source, which irradiates the LCD device from the side opposite to the viewer with respect to an LCD panel, generally refers to a back light module.
The back light module generally includes a light guide plate and a spontaneous light source, such as a lamp or a light emitting diode. The light guide plate reflects and scatters light from the spontaneous light source, making the light become a uniform surface light, so that most of the lights from the lamp are uniformly incident to the LCD panel.
Conventionally, the light source of the back light module is always in an ON state of maximum brightness level during the operation of the LCD device. However, when only some regions of the LCD device are used to display data, activating the maximum brightness level of the light source to illuminate the entire display area becomes a waste of power. For example, when the mobile phone is in a standby mode or an idle mode, a user only needs to check the caller identification or the phone number shown in a small region with respect to the display area before receiving any incoming call. Therefore, keeping the light source at its maximum brightness level consumes much more power resulting in the shortening intervals between replacing batteries.
Therefore, there is a need to provide a display apparatus with less power consumption.